Description: (Abstract Provided by Applicant) Heterosexual transmission of HIV is responsible for more than 90% of the HIV infections occurring in the world. Women, compared with men, experience at least an eight-fold higher risk of HIV infection following vaginal intercourse. However, our understanding of how HIV infection occurs in the lower female genital tract remains rudimentary. For example, the identity of the first cell infected within the vaginal mucosa is controversial (Langerhans cell versus subepithelial dendritic cell). Transcytosis of virus through the epithelium may also occur and subepithelial dendritic cells expressing DC-SIGN may simply bind and ferry HIV to regional lymph nodes in the absence of active viral replication. We now propose to systematically study the molecular and cellular basis for heterosexual transmission of HIV by inoculating a cervical vaginal organ culture system with green fluorescent virions. We will monitor how these virions navigate across this mucosal surface and identify the initial cellular targets of interaction or infection. We will also study isogenic viruses differing only in their chemokine receptor tropism (CCR5 versus CXCR4) exploring whether the preferential transmission of R5-tropic viruses between humans is restricted at the level of the mucosal surface. We will analyze matched viruses containing clade E versus clade B env genes testing the clinical suggestion that clade E viruses spread more efficiently by heterosexual transmission. Additionally, we will compare the infectivity of viruses containing mutations in the protease gene induced by potent protease inhibitors or in the nef gene linked to the selective loss of CD4 or MHC class I receptor downregulation. Finally, we will evaluate whether treatment of the cervical vaginal organ cultures with estrogen or progesterone reproducibly influences their susceptibility to infection with HIV (Specific Aim 1). In a second line of investigation, we will explore the unexpected ability of the HIV-1 Vpr gene product to function as a transcriptional coactivator with the glucocorticoid receptor testing whether Vpr similarly coactivates estrogen, progesterone, or androgen nuclear hormone receptor activity. We will also examine whether these hormones alone or in combination with Vpr alter transcriptional activity of the HIV-1 LTR in the context of normal chromatin structure or induce the activation of HIV replication in latently infected cells (Specific Aim 2). Finally, we will explore the protein-transducing properties of soluble Vpr that permit this protein to efficiently enter and function in uninfected host cells. Synthetic, full-length soluble Vpr will be tested for coactivating effects with the glucocorticoid receptor when added extracellularly and analyzed for its ability to enhance progesterone mediated inhibition of MIPl-a. MIPl-b, and RANTES antiviral chemokine secretion by activated CD8+ T cells (Specific Aim 3). Through these studies, we seek to gain a clearer understanding of the biology underlying heterosexual transmission of HIV in women and the potential interplay of HIV Vpr with various female sex hormones that may modify the replication potential of the virus in a gender specific manner or alter the local permissiveness of the cervical vaginal mucosa to virus infection.